The present invention generally relates to a method of determining a thickness of a layer on a semiconductor wafer, and more particularly to a method of determining the thickness of opaque layers. The present invention further relates to a system for determining a thickness of a layer on a semiconductor wafer.
There are several semiconductor wafer processing techniques in which thin layers or films are deposited and/or removed. These techniques could be improved by the knowledge of the layer thickness. Frequently, optical techniques are used to determine the layer thickness. However, these techniques only work for measuring transparent layers.
For example, electroplating is an emerging process technology being used to facilitate the deposition of copper films to integrated circuit structures. The technology of electroplating is currently limited by the lack of process control mechanisms including deposition termination. The process is typically performed with timed process steps which does not guarantee a deposition with accurate thickness.
As another example, plasma etch tool technology is currently limited by endpointing schemes that are not directly based on film thickness targets but on indirect methods. Such indirect methods are, for example, optical emission spectroscopy, or timing methods that are based on previously run test wafers. Further, as the film thickness is decreasing, interferometry may be used as an indirect endpoint determination.
Also wet tool technology is currently limited by endpointing schemes that are not directly based on film thickness targets. Also in this case, timed methods based on previously run test wafers are used.
Similarly, in diffusion process technology, indirect methods are used. Also in this case, interferometry, or timed methods based on previously run test wafers are employed.
Further technologies in which the thickness of layers on a wafer is of interest are chemical vapor deposition (CVD) and physical vapor deposition (PVD). Also in these processes, the current measurement technology is limited by a lack of control mechanisms.
The present invention seeks to solve the above mentioned problems by providing a new method and a new system for reliably and accurately determining a thickness of a layer on a semiconductor wafer.